We are in the process of determining the in vivo post-translational modifications of human lens crystallins that occur with cataractogenesis and normal aging. We have developed an HPLC/MS procedure to screen crystallin fractions for post-translational modifications. After a modified crystallin is identified, this fraction is enzymatically digested and analyzed by HPLC/MS to identify the modified peptides, which are then isolated and analyzed by MS/MS to determine the nature and location of the post-translational modification.